In optical communications networks, optical transceiver modules are used to transmit and receive optical signals over optical waveguides, which are typically optical fibers. An optical transceiver module includes a transmitter (Tx) portion and a receiver (Rx) portion. In the Tx portion, a light source is modulated based on an electrical data signal and generates corresponding optical data signals. An optical coupling system of the optical transceiver module optically couples the optical data signals into an end of an optical fiber. The light source is typically a laser diode, but is sometimes a light emitting diode (LED). In the Rx portion of the optical transceiver module, a photodetector, which is typically a photodiode, detects optical data signals transmitted over an optical fiber and converts the optical data signals into electrical data signal, which are then amplified and processed by electrical circuitry in the Rx portion to recover the data.
In typical small form factor (SFF) optical transceiver modules and small form factor pluggable (SFP) optical transceiver modules, a transmit optical fiber is connected to the Tx portion of the module and a receive optical fiber is connected to the Rx portion of the module. Optical data signals generated in the Tx portion are transmitted over the transmit fiber and optical data signals transmitted over the receive optical fiber are received in the Rx portion. In such modules, the Tx and the Rx portions typically include respective optical coupling systems for coupling optical signals between the laser diode and photodiode of the Tx portion and Rx portion, respectively, and the transmit optical fiber and the receive optical fiber, respectively.
In contrast to the typical known SFF and SFP optical transceiver modules, optical transceiver modules are also known that use a single fiber for bi-directional communications. In these single-fiber optical transceiver modules, a single optical fiber is used for transmitting optical data signals produced by a laser diode of the module and for receiving optical data signals transmitted over the fiber on a photodiode of the module. In most of these single-fiber optical transceiver modules, the laser diode IC and the photodiode IC are spatially separated in the modules. In these modules, various types of optical coupling systems are used to optically couple the transmitted and received optical data signals between the laser diode and the photodiode, respectively, and the end of the optical fiber. The spatial arrangement of the laser diode and the photodiode and the configuration of the optical coupling systems are typically designed to prevent optical crosstalk between the laser diode and the photodiode, while also providing adequate optical coupling efficiency for the transmitted and received light being coupled between the laser diode and the photodiode, respectively, and the end of the optical fiber.
Although spatially separating the laser diode and the photodiode from each other helps to reduce optical crosstalk, relatively complex optical coupling systems are typically needed to ensure that there is good optical coupling efficiency for the transmitted and received optical data signals. The use of relatively complex optical coupling systems increases the overall cost of the module, while spatially separating the laser diode and the photodiode increases the overall size of the module.
It is also known in single-fiber optical transceiver modules to co-locate, or stack, the laser diode and the photodiode together, or even to integrate them into the same IC package. However, such arrangements typically also require the use of relatively complex optical coupling systems to prevent optical crosstalk between the laser diode and the photodiode. In addition, in such arrangements, stacking of the photodiode and the laser diode or LED or integrating them together typically reduces the amount of effective area on the photodiode that is available for light absorption due to the fact that the laser diode or LED blocks a portion of the received light. Therefore, in such arrangements, the optical coupling efficiency for the received light may be less than adequate unless other precautions are taken to enhance the optical coupling efficiency. In addition, in such arrangements it is often necessary that a laser diode be used instead of an LED due to the fact that a laser diode produces a smaller optical far field than that produced by an LED. The smaller optical far field of the laser diode helps reduce optical crosstalk between the laser diodes on each end of the optical link.
A need exists for a single-fiber optical transceiver module in which the photodiode and the laser diode or LED can be co-located, that has high receive and transmit optical coupling efficiency, that is configured to reduce optical crosstalk, and that uses a relatively simple optical coupling system.